1. Field of the Invention
The present invention relates to a photo sensor type touch panel, and more particularly, to a photo sensor type touch panel including a plurality of readout lines electrical connected in parallel and having equal coupling capacitors between the readout lines and adjacent data lines of different polarity types.
2. Description of the Prior Art
The touch panel has been prevalently used in the input interfaces of the instruments for its properties such as the diversification for design and the interaction between machines and humans. According to the different input mechanism, the touch panel can be classified to resistive type, capacitive type, electromagnetic type, and optical type. The optical type touch panel can be further divided into optical imaging type and photo sensor type. On the other hand, according to different integration designs for the touch panel and the display panel, the touch panel can be classified to out-cell type and in-cell type touch panel. Among aforementioned touch techniques, the photo sensor type touch panel has possessed the greatest market potential due to its advantages of multi-touch function and convenience to be integrated into display panel fabrication.
The photo sensor type touch panel includes photo sensing devices for detecting illumination intensity and for generating touch signals, and readout lines for reading the touch signals. The photo sensing devices and the readout lines are fabricated on the array substrate of the display panel, together with the thin film transistors (TFTs) and the pixel electrodes. The readout line is disposed in between two adjacent data lines and thus a coupling capacitor is respectively formed between the readout line and the two adjacent data line. Consequently, the data signals from the data lines and the touch signals from the readout lines suffer variations due to the impact from the coupling capacitor. Furthermore, since the capacitance of the two coupling capacitors are not equal, the capacitance of the coupling capacitor between the readout line and the adjacent data lines at frame time N is not equal to the capacitance of the coupling capacitor between the readout line and the adjacent data lines at frame time N+1 when the data lines of the display panel adopt column inversion driving approach, particularly when high gray level images are displayed. In other words, because of the influence from the coupling capacitor, the signal read out by the readout lines may be recognized positive at one frame time (such as frame time N) while another signals read out by the readout lines may be recognized negative at another frame time (such as frame time N+1). Therefore, the track of touch points suffers non-continuance issue, that is the broken line issue, during user's manipulations. Accordingly, the touch panel is blamed for inferior detection accuracy.